Electrical stimulation technology is expanding in scope, resulting in therapies that implant leads in more and more areas of the body. However, before undergoing complex surgery associated with permanently implanting an electrical signal generator and medical lead, a patient or their health care provider may want to determine whether the patient may be responsive to therapy associated with such implantable medical systems.
Temporary or trial leads may be employed to determine whether a patient is a candidate for electrical stimulation therapy. The temporary lead can be implanted in the patient such that a distal end containing an electrode is positioned in proximity to a tissue to which the therapeutic electrical signal is to be delivered. The proximal end of the lead remains external to the patient and can be connected to an external signal generator so that electrical signals may be delivered to the target tissue via the lead.
One therapy where trial leads are currently employed is sacral nerve stimulation. Currently unipolar leads with a single electrode are used for trialing purposes to determine whether the patient would be a good candidate for therapy with an implantable electrical signal generator. A ground pad is adhered to the skin of the patient to complete the circuit and allow the temporary trial therapy to be tested. If the ground pad falls off the patient's skin, the circuit cannot be completed and the therapy cannot be effectively tested. Bipolar trialing leads and systems would be desirable. However, as additional wires are added to the leads to couple electrodes to contacts designed to electrically couple the lead to the trial stimulator, the thickness and complexity of the lead increases.
The thickness of the trialing lead can be determinative as to whether the temporary lead is implanted in a physician's office or in the operating room. For purposes of convenience and cost, it is often desirable to implant a lead in a doctor's office as opposed to an operating room. While there are no clear guidelines regarding where an implant procedure is to be performed, physicians are often uncomfortable implanting a temporary lead if an introducer having a gauge smaller than (or thicker than) a 20-gauge needle. The inner diameter of typical 20-gauge needles is about 0.035 inches (about 0.9 millimeters). Thus, it is desirable to keep trialing leads to a diameter of less than about 0.03 inches (about 0.75 millimeters). Adding additional contacts, electrodes, and wires to make a bipolar trialing lead, while maintaining a small profile, presents a difficult challenge.